Detailed analysis of the humoral immune response to ribosomal P and other protein antigens indicate that self antigen initiates and/or maintains autoantibody production in SLE. This proposal will extend these studies to investigate the role of self antigen in the SCID adoptive transfer model and examine anti-P immunoglobulin gene utilization. With increasing evidence to support the presence of antigen specific T cells, a major emphasis will be placed on characterization of the ternary complex responsible for T cell recognition of the P proteins. The following specific questions will be addressed: 1. To explore the role of self antigen in autoantibody production, SCID mice will be engrafted with SLE PBMC and immunized with the P proteins or a control antigen. The levels of anti-P will be compared between the two groups. To examine whether autoantibody production is T cell dependant in this model, T cells and T cell subsets will be depleted in vivo in SCID mice adoptively transferred with SLE PBMC. 2. Further evidence for antigen-reactive T cells will be sought by quantifying cytokine mRNA expression following exposure to P protein antigens. Particular emphasis will be placed on inhibitory cytokines which may explain the Th2-like response of patients with SLE. Components of the ternary complex (antigenic peptides and MHC class II alleles) will be characterized. 3. To determine whether human autoantibodies are derived from an unusual B cell subset are clonally related/are somatically mutated, single chain Fv fragment antibodies will be cloned from recombinatorial libraries. The Ig VL and VH genes will be sequenced and compared between clones and between individuals. The antibodies will be used to generate anti-id reagents. If successful, the information obtained in the current proposal will provide insight into several B cell abnormalities in SLE including direct evidence for antigen drive and the identification of autoantibody genes. Characterization of the ternary complex would allow the dramatic advances in therapy of experimental autoimmune diseases (EAE, collagen arthritis) to be applied to SLE.